General Motors Inc and Lyft Inc Monday announced an alliance to develop an on-demand network of autonomous vehicles as well as a $500 million investment by the automaker as part of a $1 billion fund-raising round by the ride-sharing service. The two companies said the partnership, which involves one of GM’s largest investments in another company, stemmed from their shared view that autonomous vehicles will first reach consumers as part of a ride-sharing service, rather than vehicles owned by drivers.